U.S. Pat. No. 4,112,177 to Salditt et al. discloses a microporous medical pressure-sensitive adhesive tape construction providing a plurality of layers of pressure-sensitive adhesive wherein the total adhesive mass is microporous. As disclosed at column 4, lines 5-9, the firm underlying layer preserves the porous nature of the adhesive mass and the "quickstick" softer outer layer of adhesive adheres very readily to the skin.
U.S. Pat. No. 4,499,896 to Heinecke discloses a wound dressing for wounds having a significant amount of exudate comprising a conformable, moisture vapor permeable, liquid water-impermeable first layer containing at least one hole therein through which exudate can pass, and an imperforate, conformable, liquid water-impermeable, moisture vapor-permeable second layer attached to the first layer and overlaying the hole or holes in the first layer. These layers form a reservoir into which the wound exudate can pass and from which the exudate can evaporate.
European Patent No. 0 257 133 to Ewell discloses a wound dressing containing a fabric layer within which is deposited a layer of a hydrophilic material. Pressure-sensitive adhesive is applied to both faces of the fabric layer. One of the pressure-sensitive adhesive layers is for adhering the dressing onto the patient. A cover layer may be additionally applied to the other pressure-sensitive adhesive layer. The layer of hydrophilic material disposed within the fabric layer is provided to absorb excess exudate from the wound.
U.S. Pat. No. 4,773,409 to Cilento et al. discloses an occlusive wound dressing which includes a flexible closed cell polyurethane foam layer having a pressure-sensitive microporous adhesive applied onto one surface of the foam. A polymeric film may be laminated to the opposite surface of the foam to protect the dressing. The foam itself contains water dispersible, water swellable and/or water absorbing agents.
U.S. Pat. No. 3,800,792 to McKnight et al. discloses a surgical dressing for treatment, particularly of burn wounds, comprising a thick layer of collagen compressed foam film which has been laminated to a thin continuous layer of an inert polymer material such as polyurethane.
U.S. Pat. No. 3,849,238 to Gould et al. discloses an artificial skin comprising a water containing hydrophilic polymer sponge layer and a thinner non-hydrophilic polymer layer which is moisture vapor permeable and gas permeable.
Wound dressings, such as foam and pouch dressings described above, that act as a reservoir for excess exudate perform a specific role in wound therapy, but are not appropriate for all wounds. These wound dressings can be disadvantageous when applied to moderately exudating wounds because, due to their capability of containing fluids, a need for changing these dressings may not be perceived by the user. Because all exudate will be contained by these dressings, they can provide an excessively wet environment for the wound which promotes the growth of bacteria. A reservoir type dressing has a limited useful lifetime on a wound because it eventually will become saturated and must be changed.
As a general rule, as the moisture vapor transmission properties of a film backing or an adhesive are improved, a sacrifice is made in another property. In the case of film backings, an increase in moisture vapor transmission will generally result in a backing with reduced tensile strength and elongation properties. A higher moisture vapor transmissive backing is also typically very sensitive to direct contact with aqueous fluids, which will result in unacceptable swelling of the film so that it no longer stays in place on the substrate. The film may also experience a dramatic loss in tensile strength when exposed to direct aqueous fluid contact.
Similarly, a highly moisture vapor transmissive adhesive will typically display shortcomings in properties such as internal cohesion, which results in residue being left on the skin after removal of the bandage, and an undesirably low level of initial and final adhesion to skin levels.
Transparent dressings currently available on the market utilizing Hytrel.TM. or Estane.TM. backings do a generally good job of protecting wounds while permitting some moisture vapor to escape from the site, but could be substantially improved with an increase in moisture vapor transmission if other strength, swell and adhesive properties were not sacrificed.